Field of the Invention
The present invention relates to a lithography apparatus and a method of manufacturing an article.
Description of the Related Art
When manufacturing a device (for example, a semiconductor element, liquid crystal display element, or thin-film magnetic head) using a photolithography technique, an exposure apparatus is used, in which the pattern of a reticle (mask) is projected to a substrate such as a wafer through a projection optical system to transfer the pattern.
Recently, exposure apparatuses are requested to manufacture not only IC chips such as a memory and logic, but also special elements (stacked devices using a through via process) such as a MEMS and CMOS image sensor (CIS). The manufacture of such a special element does not require a high line width resolution and overlay accuracy, but requires a large depth of focus, compared to the manufacture of a conventional IC chip.
When manufacturing a special element, a special process is performed to expose the upper surface side of a substrate (for example, an Si wafer) based on an alignment mark formed on the lower surface side of the substrate. This process is necessary to, for example, form a through via from the upper surface side of a substrate and electrically connect the upper surface side to a circuit on the lower surface side of the substrate. Nowadays, technical support for detection (to be referred to as a “lower surface alignment” hereinafter) of an alignment mark formed on the lower surface side of a substrate is becoming important. Especially when exposing the upper surface side of a substrate based on an alignment mark formed on the lower surface side of the substrate, overlay inspection needs to be performed between an alignment mark formed on the upper surface side of the substrate and an alignment mark formed on the lower surface side.
As the lower surface side alignment, Japanese Patent Laid-Open No. 2002-280299 has proposed a technique in which an alignment detection system is constituted on the lower surface side (substrate chuck side) of a substrate. However, when the alignment detection system is constituted on the lower surface side of a substrate, it can detect only alignment marks positioned in the detection region of the alignment detection system, and cannot detect alignment marks positioned at arbitrary positions on the substrate.
Japanese Patent Laid-Open No. 2011-40549 has proposed a technique of detecting an alignment mark formed on the lower surface side of a substrate from the upper surface side of the substrate by using infrared light (light having a wavelength of 1,000 nm or more) that can be transmitted by a substrate.
In general overlay inspection in the exposure apparatus, inner and outer marks formed on the same layer of a substrate are simultaneously detected to obtain the amount of overlay shift between the inner and outer marks. This is because the focus position of an alignment detection system can be adjusted to both the inner and outer marks. A substrate stage that holds a substrate need not be driven in the Z-axis direction (optical axis direction of the alignment detection system) at an interval between detection of the inner mark and detection of the outer mark. Hence, high-accuracy overlay inspection can be implemented.
When manufacturing a special element, it is necessary to perform overlay inspection of an alignment mark (lower surface side mark) formed on the lower surface side of a substrate and an alignment mark (upper surface side mark) formed on the upper surface side of the substrate, as described above. However, the lower surface side mark and upper surface side mark are not formed on the same layer of the substrate and thus cannot be detected simultaneously.
To solve this, in Japanese Patent Laid-Open No. 2011-40549, the upper surface side mark is detected with light (visible light) shorter in wavelength than infrared light. After the substrate stage that holds the substrate is driven in the Z-axis direction, the lower surface side mark is detected with infrared light. In this manner, overlay inspection of the lower surface side mark and upper surface side mark is performed. In this case, however, the focus position of the alignment detection system differs between detection of the upper surface side mark and detection of the lower surface side mark, and needs to be adjusted to each of the upper surface side mark and lower surface side mark. To do this, the substrate stage needs to be driven twice, or the focus adjustment lens of the alignment detection system needs to be driven twice. The accuracy of overlay inspection between the lower surface side mark and the upper surface side mark drops owing to the driving error of the substrate stage or focus adjustment lens.
The alignment detection system may be designed to generate axial chromatic aberration between visible light and infrared light in correspondence with the substrate thickness. This makes it possible to detect the upper surface side mark and the lower surface side mark with visible light and infrared light without driving the substrate stage in the Z-axis direction. In this case, however, overlay inspection can be performed for only a substrate of a predetermined thickness, and cannot cope with a change of the substrate thickness.